1. Field of the Invention
The present invention pertains to an aluminum oxide (Al.sub.2 O.sub.3) based ceramic which has great strength and toughness, and exhibits excellent performance when used in cutting tools under severe conditions.
2. Prior Art
Japanese Patent Application laid open with Publication No. 53-118410 describes a conventional Al.sub.2 O.sub.3 based ceramic which is manufactured by the following method. First, Al.sub.2 O.sub.3 powder, powders of metal oxides and powders of hard dispersed phase constituents are prepared as starting powders. The metal oxides serving as the binder phase constituents are selected from those of yttrium (Y), magnesium (Mg), chromium (Cr), cobalt (Co), nickel (Ni) and rare earth elements (abbreviated to R), while the hard dispersed phase constituents are carbides (MC), nitrides (MN), carbo-nitrides (MCN), oxy-carbides (MCO), oxy-nitrides (MNO), oxy-carbo-nitrides (MCNO) of the metals (M) of the Group IVa of the Periodic Table (hereinafter referred to as M(CNO)). No more than 10% by weight of one or more metal oxide powders, 10 to 90% by weight of one or more M(CNO) powders, and balance Al.sub.2 O.sub.3, are blended and compacted into a green compact under conventional conditions. Thereafter, the compact is subjected to hot pressing at a temperature of 1580.degree. C., a pressure of 30 atm. and a holding time of 10 to 30 minutes. The resulting ceramic has a composition substantially equal to the blending composition of the powders, and the metal oxide forms the binder phase thereof while Al.sub.2 O.sub.3 and M(CNO) define the hard dispersed phase.
The aforesaid Al.sub.2 O.sub.3 ceramic is, however, insufficient for use in cutting tools. More specifically, as the demands for labor saving, higher performance and higher speed operation increase in various industrial fields, the conditions under which the cutting tools are put to use are also becoming severe. Thus, cutting tools are now required to have greater strength and toughness. However, the aforesaid Al.sub.2 O.sub.3 ceramic, as well as the other kinds of ceramics, are susceptible to fracture or chipping due to insufficient strength and toughness when used under severe conditions.